The brown lanternshark or bristled lanternshark (''Etmopterus unicolor'') is a little-known species of deep-sea

dogfish shark Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned ...

in the family

Etmopteridae The Etmopteridae are a family of sharks in the order Squaliformes, commonly known as lantern sharks. Their name comes from the presence of light-producing photophores on their bodies. The members of this family are small, under long, and are ...

. It is found off

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

and

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, and possibly also

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, typically deeper than . This species can be distinguished from other lanternsharks by its coloration, which is a uniform dark gray or brown without the ventral surface being much darker and clearly delineated from the rest of the body. The brown lanternshark feeds on small

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

es,

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s, and

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. Reproduction is

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparity, oviparous and live-bearing viviparity, viviparous reproduction. Ovoviviparous animals possess embryos that develo ...

, with females giving birth to 9–18 young. An unusually high proportion of individuals in

Suruga Bay Suruga Bay (駿河湾, ''Suruga-wan'') is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of a straight line from Omaezaki Point to Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honsh� ...

are

hermaphrodite A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

s, with both male and female characteristics.

Taxonomy

The brown lanternshark was first described by Robert Engelhardt as ''Spinax unicolor'' in 1912, in the scientific journal ''Zoologischer Anzeiger''. The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

was a 55-cm-long female from

Sagami Bay lies south of Kanagawa Prefecture in Honshu, central Japan, contained within the scope of the Miura Peninsula, in Kanagawa, to the east, the Izu Peninsula, in Shizuoka Prefecture, to the west, and the Shōnan coastline to the north, while the i ...

. In 1965, Tokiharu Abe redescribed this species and moved it to the genus ''Etmopterus''. The Australian ''Etmopterus'' "sp. B" (known as the "bristled lanternshark") is now tentatively believed to be the same as this species. It is grouped with the

velvet belly lantern shark The velvet belly lanternshark (or simply velvet belly) (''Etmopterus spinax'') is a species of dogfish shark in the family Etmopteridae. One of the most common deepwater sharks in the northeastern Atlantic Ocean, the velvet belly is found from Ic ...

(''E. spinax''), Caribbean lanternshark (''E. hillianus''),

fringefin lanternshark The fringefin lanternshark (''Etmopterus schultzi'') is a shark of the family Etmopteridae found in the western central Atlantic from Texas to Florida, northern Gulf of Mexico, and Mexico. It is endemic to this area. It is a deep water shark and ...

(''E. schultzi''),

broadbanded lanternshark The broadbanded lanternshark (''Etmopterus gracilispinis'') is a shark of the family Etmopteridae found in the western and southeast Atlantic, between latitudes 40°N and 45°S, at depths of between 70 and 1,000 m. Its length is up to 35 ...

(''E. gracilispinis''), combtooth lanternshark (''E. decacuspidatus''), and

dwarf lanternshark The dwarf lanternshark (''Etmopterus perryi'') is a species of dogfish shark in the family Etmopteridae and is the smallest shark in the world, reaching a maximum known length of . It is known to be present only on the upper continental slopes of ...

(''E. perryi'') in having irregularly arranged, needle-shaped

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

s. ''Etmopterus compagnoi'' is a questionably valid species as it may be based on the brown lanternshark or ''

Etmopterus baxteri The New Zealand lanternshark (''Etmopterus baxteri'') is a shark of the family Etmopteridae mainly found off the coast of New Zealand. It can also be found in the Southern areas of Australia and Africa, inhabiting water depths between 500-1500m. ...

''.

Distribution and habitat

Confirmed specimens of the brown lanternshark have been captured from off southern

Honshu , historically known as , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the list of islands by area, seventh-largest island in the world, and the list of islands by ...

, Japan, and around New Zealand. If ''E. compagnoi'' and ''E.'' sp. B are also considered, then the known range of this species is extended to off South Africa (and possibly southern

Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

) and southern Australia. The brown lanternshark inhabits

continental shelves A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

and

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

s at a depth of , though is most common below . It is generally found deeper than other lanternsharks that share its range, and may have midwater habits.

Description

The brown lanternshark has a robust, almost cylindrical body with a wide, flattened head. Around 28 tooth rows are in the upper jaw and 34 tooth rows are in the lower jaw. The upper teeth have a pointed central cusp flanked by fewer than three pairs of lateral cusplets, while the bottom teeth are large and tipped with a strongly angled triangular cusp. The five pairs of

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...

s are relatively large. The first

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

is low with a minute leading spine; the second dorsal fin is twice as high as the first with a much larger spine. The

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

is short, leading to a long

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

with the upper lobe much larger than the lower. The dermal denticles of this shark are tiny and densely placed with no regular pattern; each denticle has a four-cornered base and rises to a narrow, slightly curved point. The denticles of females are firmly attached, while those of males are easily removed. The coloration is a plain dark gray or brown, slightly darker below and lighter on the dorsal fin margins. Unlike other lanternsharks, there is a not a sharp contrast between the dorsal and ventral colors. There is a horizontal black line on the base of the tail, and another fainter black mark over the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s. The maximum reported length is for males and for females.

Biology and ecology

The most important prey of the brown lanternshark are bony fishes (mainly

lanternfish Lanternfish (or myctophids, from the Greek language, Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family (biology), family Myctophidae. One of two families in the order Myctophiformes, ...

es), followed by cephalopods (mainly the

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

'' Watasenia scintillans''), and finally crustaceans (mainly

prawn Prawn is a common name for small aquatic crustaceans with an exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the intern ...

s such as ''Acanthephyra''). A known

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

of this shark is a species of

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

in the genus ''Lerneopoda''. Like other lanternsharks, the brown lanternshark is ovoviviparous, meaning the young hatch inside the mother's

uterus The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...

and are sustained by a

yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...

. The litter size is 9–18. Newborns measure in length. Males reach

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized ...

at a length of , and females at a length of . A study of brown lanternsharks in

by Yano and Tanaka (1989) found a 23% prevalence of hermaphroditism within the population. Of the 16 hermaphrodites examined, 15 were functional females (and some were pregnant) that also possessed well-developed

claspers In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's c ...

(male

intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs ...

s), while one was a functional male with

ovarian The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endoc ...

tissue in the left

testis A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...

. The reason why so many sharks in Suruga Bay are hermaphroditic is unclear, but has been speculated to relate to

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

Human interactions

Although it may be caught as bycatch and discarded, the brown lanternshark is harmless and of no significance to

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

. Its conservation status has not been evaluated beyond Data Deficient by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

. In June 2018 the New Zealand

Department of Conservation Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrative division), a geographical and administrative division within a country, ...

classified the brown lanternshark as "Not Threatened" with the qualifier "Secure Overseas" under the

New Zealand Threat Classification System The New Zealand Threat Classification System is used by the Department of Conservation to assess conservation priorities of species in New Zealand. The system was developed because the IUCN Red List, a similar conservation status system, had s ...

References

{{Taxonbar, from=Q3760674 Etmopterus Taxa named by Robert Engelhardt Fish described in 1912 Marine fish of New Zealand